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Abstract:

A method to control a gas engine system is disclosed, whereby the engine
can be operated with an air-fuel-ratio controlled with high precision,
even in using a low calorific fuel-gas that is prone to vary in calorific
value; the engine system includes: a first gas line toward each
cylinder via a first gas valve from a gas supply source line, the first
gas valve regulating flow rates of the fuel-gas through a gas compressor
on the line; a second gas line toward suction air, the line being
branched from the gas supply source line and the line being provided with
a gas air mixer and a second gas valve on the line.
In the case when the fuel-gas is of a low calorific value or where the
output of the engine is high, a part of the fuel-gas is supplied to the
engine through the first and second lines. The mixer forms a mixture of a
prescribed mixing ratio that is leaner than a lower limit of flammability
of the fuel-gas, while the remaining fuel-gas through the first line is
supplied to the mixture just before each cylinder so that a final
prescribed air fuel ratio is formed.
In the case when the calorific value of the fuel-gas is high, or of high
engine output, the whole fuel-gas can be supplied only through the first
gas line.

Claims:

1. A method to control a gas engine that ignites and burns fuel-gas, the
gas engine comprising:a turbocharger that pressurizes ambient air and
supplies the air to the engine to a plurality of cylinders;a first gas
supply line, with a branch line coming off it for each cylinder;a first
gas valve for each cylinder, the valve being fitted on the gas supply
branch line and being able to regulate the flow rate of the fuel-gas
toward each cylinder;a gas compressor that is provided on the first gas
line that compresses the fuel-gas toward the first gas valve through the
first gas line so that the pressure through the first gas line exceeds a
pressure boosted by the turbocharger;whereby, the fuel-gas through the
first gas line and the air through the turbocharger are mixed to form an
air gas mixture;and, in the case when the fuel-gas is of a low calorific
value, or in the case when an output of the engine is high, the engine
further comprises:a second gas line toward suction air before the
turbocharger the line which is branched from the gas supply source line;a
second gas valve for the suction air the valve which is provided on the
second gas line toward the suction air before the turbocharger, and is
regulated with on-off movements;an air gas mixer that is provided on the
upstream air inflow line of the suction air toward the turbocharger, and
mixes the fuel-gas through the second gas line with the ambient air
induced toward the turbocharger;whereby, the fuel-gas and the air are
mixed so as to form a mixture of a prescribed mixing ratio that is leaner
than a lower limit of flammability as to the fuel-gas, and the air
fuel-gas mixture is supplied to the turbocharger, while the remaining
fuel-gas that is not supplied to the mixer from the gas supply source
line is sent to each cylinder through the gas compressor and through the
first gas line toward each cylinder, so that a prescribed air fuel ratio
is formed in each cylinder by regulating the first gas valve for each
cylinder;and, in the case when the fuel-gas is of a high calorific value,
or in the case when an output of the engine is low, the second gas valve
for suction air is closed so that the whole fuel-gas from the gas supply
source line is directed toward each cylinder through the first gas line.

2. The method to control a gas engine according to claim 1, the engine
further comprising:a means to detect opening levels of the first gas
valve; anda means to detect output levels of the engine;whereby, in
response to the detected opening levels and the output levels, the second
gas valve for the suction air is opened with an estimation that the fuel
gas is of a low calorific value or the higher output of the engine is
being required, in the case when the first gas valve for each cylinder is
fully opened and the output of the engine is increasing.

3. The method to control a gas engine according to claim 1, the engine
further comprising:a means to detect opening levels of the first gas
valve; anda means to detect output levels of the engine;whereby, in
response to the detected opening levels and the output levels, the second
gas valve for the suction air is closed with an estimation that the
fuel-gas served for operation has changed into a fuel of a high calorific
value or the output of the engine is reduced, in the case when the
detected output of the engine becomes low and less than a prescribed
value.

4. A gas engine and a gas engine system thereof that ignites and burns
fuel-gas, the gas engine comprising:a turbocharger that pressurizes
ambient air and supplies the air to the engine to a plurality of
cylinders;a charging air flow-rate control valve such as an exhaust gas
by-pass valve that controls the flow rate of the charged air through the
turbocharger into the cylinders, the control valve serving as a means to
determine air flow rates when a prescribed air fuel ratio is achieved;a
first gas line toward the cylinders, the line communicating a gas supply
branch arm pipe that is provided in front of each cylinder, with a gas
supply source line;a first gas valve for each cylinder, the valve being
fitted on the gas supply branch arm pipe, the valve being able to
regulate the flow rates of the fuel-gas toward each cylinder, through the
first valve the valve acting as a fuel gas injector that injects fuel-gas
into air boosted by the turbocharger, in front of each cylinder, so that
the first gas valve injects a prescribed amount of fuel-gas in order to
produce a to-be-burnt air fuel-gas mixture of a prescribed air fuel
mixture;a gas compressor that is provided on the first gas line that
compresses the fuel-gas toward the first gas valve through the first gas
line so that the pressure through the first gas line exceeds a pressure
boosted by the turbocharger;whereby, the engine further comprises:a
second gas line toward suction air before the turbocharger the line which
is branched from the gas supply source line;a second gas valve for the
suction air the valve which is provided on the second gas line toward the
suction air before the turbocharger, and is regulated with on-off
movements;an air gas mixer that is provided on the upstream air inflow
line of the suction air toward the turbocharger, and mixes the fuel-gas
through the second gas line with the ambient air induced toward the
turbocharger;whereby, the fuel-gas and the air are mixed so as to form a
mixture of a prescribed mixing ratio that is leaner than a lower limit of
flammability as to the fuel-gas, and the air fuel-gas mixture is supplied
to the turbocharger, while the remaining fuel-gas that is not supplied to
the mixer from the gas supply source line is sent to each cylinder
through the gas compressor and through the first gas line toward each
cylinder, so that a prescribed air fuel ratio is formed in each cylinder
by regulating the first gas valve for each cylinder.

5. The gas engine and a gas engine system thereof according to claim 4,
whereby the air gas mixer is of a venturi type, the mixer mixing the
suction air with the fuel-gas through the second gas valve and the second
gas line so that an air fuel mixture of a prescribed air fuel-gas ratio
is achieved.

Description:

BACKGROUND OF THE INVENTION

[0001]1. Technical Field

[0002]The present application relates to a method to control a gas engine
and a gas engine system thereof, the engine being provided with: either a
turbocharger or a supercharger through which air is supplied to the
engine [henceforth in this application, whenever the word `turbocharger`
appears, it could equally well be replaced by `supercharger`]; a first
gas control valve that controls flow-rates of fuel-gas to be supplied to
each cylinder of the engine; whereby, the fuel-gas that is regulated by
the first gas valve and the air that is supplied through the turbocharger
are mixed so as to form a prescribed air-fuel ratio; and, the engine
burns the supplied fuel-gas under conditions of the prescribed air-fuel
ratio; specifically, the engine can be operated based on the
air-fuel-ratio control with high precision, even in the case when a low
calorific fuel gas that is prone to vary in calorific value is used.

[0003]2. Description of the Related Art

[0004]A conventional small gas engine, such as an engine with a cylinder
bore of approximately 200 mm or less, usually adopts a fuel-gas mixing
system in which fuel-gas and air are mixed upstream of air-inflow before
a turbocharger, while the fuel-gas air mixture is supplied to the main
combustion chambers i.e. cylinders, through the turbocharger (i.e., a
compressor thereof) and an air cooler.

[0005]On the other hand, in conventional larger gas engines, fuel-gas is
supplied into each cylinder, through a charging air inlet branch arm pipe
just before each cylinder and through a gas supply control valve for each
cylinder, as fuel-gas supply is required to be uniform all over the
cylinders in amount as well as in gas concentration distribution, as a
rule. In this manner, not only the air fuel ratios and the fuel
quantities over the cylinders can be equalized but also the fuel-gas
charging is streamlined; further, since fuel-gas and air are mixed just
in front of each cylinder, the length of potentially flammable
gas-air-mixture flow that is formed upstream of each cylinder can be
shortened so as to enhance engine operational safety against explosion
risks.

[0006]Hereby, it is noted that the above-mentioned gas supply control
valve for each cylinder is also called a first gas valve in this
specification; and, the first gas valve is often termed a gas admission
valve in the larger gas engine field, because it is the valve which is
provided at each cylinder of the gas engine in principle; on the other
hand, as described later in this specification, a term, namely, a second
gas valve, is introduced for a fuel-gas supply control valve that
supplies fuel-gas to suction air. Further, a fuel-gas supply line that is
connected to the first gas valve is called a first gas line in this
specification; in the same way, a second gas line is defined in response
to the second gas valve.

[0007]A patent reference 1 (JP2001-132550) discloses a technology in which
fuel-gas supply methods of the mentioned smaller and larger gas-engines
are combined. In a gas engine according to the reference 1, fuel-gas
pressurized by means of a gas compressor is supplied to a cylinder inlet
of a charging air passage or a cylinder, whereas fuel-gas that is not
compressed by the compressor is supplied to the upstream side of
air-inflow line before a turbocharger, from a gas inflow line (a gas
source) before the gas compressor; further, the fuel-gas supply can be
switched from the line toward the cylinder inlet, to the line toward the
upstream side of the air-inflow line before the turbocharger and vice
versa.

[0008]In the larger gas engine in which fuel-gas is supplied to a cylinder
inlet of a charging air passage or a cylinder, it is required that the
fuel-gas pressure at the inlet of the cylinder be higher than the
supercharged air pressure. As a result, in the case when a low calorific
fuel gas i.e. a gas of a low calorific value such as coal mine
methane-gas, a gas compressor of a large capacity is needed so as to
compress a fuel-gas of low pressure (substantially less than an ambient
pressure) and large flow rates.

[0009]On the other hand, in a gas engine with a fuel supply system in
which fuel-gas is supplied to the upstream side of the air in-flow line
before the turbocharger, a flammable air fuel-gas mixture is compressed
into a state of high temperature and a high pressure in response to a
substantially adiabatic compression process through the turbocharger
compressor; hence, potential risks of gas explosion are involved so long
as the mentioned fuel supply system is employed.

[0010]Against the above backdrop, a patent reference 2 (JP2006-244954)
discloses a technology as to a gas supply device and an operation method
thereof for the aforementioned larger gas engines. In the technology
according to the reference 2, the fuel-gas device comprises:

[0011]a second fuel-gas supply line, i.e. a second gas line, through which
a part of fuel-gas is mixed with air that is inducted by the turbocharger
compressor;

[0012]a first fuel-gas supply line, i.e. a first gas line, through which
the remaining part or the whole part of fuel-gas is mixed with air or
air-fuel mixture at a gas supply branch arm pipe upstream of each
cylinder;

[0013]a gas supply control valve, i.e. a second gas valve, for suction
air, the valve regulating fuel-gas amount (flow rates) to be supplied
through the turbocharger compressor;

[0014]a gas supply control valve, i.e. a first gas valve, for each
cylinder, the valve regulating fuel-gas amount (flow rates) to be
supplied through the gas supply branch arm pipe upstream of each
cylinder;

[0015]a gas (fuel-gas) compressor that is provided at the upstream side of
the first fuel-gas supply line;

[0016]whereby the amount (flow rates) of the fuel-gas through the second
gas line is controlled by means of regulating opening levels of the
second gas valve for suction air, so that the concentration of the
supplied fuel-gas in the air fuel-gas mixture that flows through the
turbocharger compressor is kept below the lower (lean) limit of
flammability as to the fuel-gas.

[0017]According to the above disclosure, potential risks of fuel-gas
explosion that may occur in the neighborhood of the turbocharger
compressor outlet are completely eliminated; further, the size and
capacity of the gas (fuel-gas) compressor that compresses fuel-gas and
supplies the fuel-gas to the gas supply branch arm pipe upstream of each
cylinder can be reduced because of reduced power consumption, even in the
case when a fuel gas with a low calorific value is used.

[0018]Hereby, it should be noted in addition that the patent reference 2
utilizes a technology originated from larger gas engines that are
provided with first gas valves in principle, whereas small gas engines
are not provided with a first gas valve fitted to each cylinder in
general; namely, a small gas engine includes a gas valve that supplies
fuel-gas toward the air suction line of the engine. The gas valve that
supplies fuel-gas toward the air suction line is termed a second gas
valve in this specification.

[0019]Further, it is also noted that the entire contents of the patent
reference 2 (JP2006-244954; Application No. 2006-244954 filed on Sep. 14,
2006 with Japanese Patent Office) are hereby incorporated by reference.

[0020]As described above, according to the reference 2, a gas engine can
be realized, whereby a sufficient amount (flow rates) of fuel-gas can be
secured and in addition, the fuel-gas compressor can be of a smaller size
and capacity. However, a further advanced technology has been
anticipated, whereby fuel-gas amount (flow rates) through the second gas
line toward the turbocharger compressor can be precisely controlled with
a simple mechanism, and the further advanced technology can provide a
control method to be applied even to the case where the calorific value
of the fuel-gas continuously varies.

SUMMARY OF THE INVENTION

[0021]In view of the above-stated conventional technology and anticipated
solutions thereof, the present disclosure is aiming at providing a method
to control a gas engine and a gas engine system thereof, whereby high
precision control of the air fuel ratio can be achieved even in the case
when a low calorific value fuel gas that is prone to vary in calorific
value is used.

[0022]In order to achieve the goals as mentioned, the present
specification discloses a method to control a gas engine that ignites and
burns fuel-gas, the gas engine comprising:

[0023]a turbocharger that pressurizes ambient air and supplies the air to
the engine, namely, to a plurality of cylinders;

[0024]a first gas line toward the cylinders, the line communicating a gas
supply branch arm pipe that is provided upstream of each cylinder, with a
gas supply source line;

[0025]a first gas valve for each cylinder, each valve being fitted on the
gas supply branch arm pipe and being able to regulate the flow rate of
the fuel-gas into each cylinder;

[0026]whereby the fuel-gas through the first gas line and the air through
the turbocharger are mixed to form an air gas mixture;

[0027]and, in the case when the fuel-gas is of a low calorific value, or
in the case when the engine is being operated at more than half load),
the engine further comprising:

[0028]a second gas line toward the turbocharger the line which is branched
from the gas supply source line;

[0029]a second gas valve for suction air the valve which is provided on
the second gas line toward the turbocharger, and is regulated with on-off
movements;

[0030]an air gas mixer that is provided on the upstream air inflow line of
the turbocharger, and mixes the fuel-gas through the second gas line with
the ambient air inducted toward the turbocharger;

[0031]whereby the fuel-gas and the air are mixed so as to form a mixture
of a prescribed ratio that is leaner than a lower limit of flammability
as to the fuel-gas, and the air fuel-gas mixture is supplied to the
turbocharger, while the remaining fuel-gas that is not supplied to the
mixer from the gas supply source line is sent to each cylinder through
the gas compressor and through the first gas line toward each cylinder,
so that a prescribed air fuel ratio is formed in each cylinder by
regulating the first gas valve for each cylinder;

[0032]and, in the case when the fuel-gas is of a high calorific value, or
in the case when an output of the engine is low, the second gas valve for
suction air is closed so that the whole of the fuel-gas from the gas
supply source line is directed toward each cylinder through the first gas
line.

[0033]According to the present invention, a part of the fuel-gas can be
supplied to the engine suction air that is inducted by the turbocharger,
in the case when the fuel-gas amount to be supplied is large as is the
case when the fuel-gas is of a low calorific value, or the engine output
is high; thus, an air fuel ratio control with precision can be realized,
while necessary fuel amount is secured. In other words, the engine is
provided with a mixer that mixes fuel-gas with the induced air so that
the concentration of the fuel air mixture is smaller than a prescribed
concentration below a lean limit of flammability as to the fuel-gas;
thus, the fuel-gas compressor that is arranged on the first gas line
toward each cylinder can be of a smaller size and capacity; further,
potential fuel-gas explosion risks in the air supply passage can be
removed; what is more, since the mixer yields an air fuel mixture of a
prescribed concentration, the air fuel control at the first gas valve for
each cylinder can be simplified.

[0034]Moreover, in another aspect of the present invention, an opening
level of the aforementioned first gas valve as well as an output of the
engine is detected during operation so that the second gas valve for
suction air is opened with an estimation that the fuel gas is of a low
calorific value or the higher output of the engine is being required, in
the case when the first gas valve for each cylinder is fully opened and
the output of the engine is increasing.

[0035]In this way, whether or not the fuel-gas supply through the mixer is
necessary can be simply and pertinently judged; thus, an air fuel control
with precision can be realized.

[0036]In another aspect of the present invention, the second gas valve for
suction air is closed with an estimation that the fuel-gas served for
operation has changed into a fuel of a high calorific value or the output
of the engine is reduced, in the case when the detected output of the
engine becomes low and less than a prescribed value.

[0037]In this way, an upper threshold value as to a maximum controllable
fuel-gas flow rate is predetermined; and, in the case when a fuel-gas
flow rate becomes less than the upper threshold value as a prescribed
value, the second gas valve for suction air is closed and the whole
fuel-gas flow rate is regulated only by means of the first gas valve for
each cylinder. Thus, the fuel-gas flow rate can be simply controlled with
precision.

[0038]Further, the present invention discloses a control device of an
engine that is provided with not only the first gas valve for each
cylinder but also a charging air flow-rate control valve such as an
exhaust gas by-pass valve that controls the flow rate of the charged air
through the turbocharger into the cylinder's, whereby the first gas valve
for each cylinder acts as a fuel-gas injector for injecting fuel-gas into
the charged air so that air fuel mixture of a required air fuel ratio is
supplied into each cylinder; wherein, the control device is further
provided with: a second gas line toward suction air before the
turbocharger the line which is branched from the gas supply source line
so as to be connected to the air inflow line toward the turbocharger
compressor, the line comprising a second gas valve for suction air, of
on-off control; a gas supply line to the cylinders the line which is
branched from the gas supply source line, the line comprising a gas
compressor that pressurizes fuel-gas so that the fuel-gas can flow into
the boosted charging air; a mixer that is provided on the upstream air
inflow line toward the turbocharger, and mixes the fuel-gas through the
second gas line, with the ambient air induced toward the turbocharger so
that the concentration of the air fuel mixture is kept lower than a
prescribed concentration below a lean limit of flammability as to the
fuel-gas;

[0039]Further, it is preferable that the mentioned mixer is of a venturi
type, and the air and the fuel-gas are mixed so that the prescribed air
fuel ratio can be achieved.

[0040]As described above, the present invention can provide a method to
control a gas engine and a gas engine system thereof, whereby an air fuel
ratio control with high precision can be achieved even in the case when a
low calorific fuel gas that is prone to vary in calorific value is used.

[0041]To be more specific, an air fuel ratio control with precision can be
realized, while necessary fuel amount is secured, in a manner that a part
of the fuel-gas is supplied to the engine suction air that is inducted by
the turbocharger, only in the case when the fuel-gas amount to be
supplied is being increased as is the case when the fuel-gas is of a low
calorific value, or the engine output is high. In other words, the gas
compressor can be of a smaller size and capacity by means of providing a
mixer that mixes fuel-gas with suction air so that the concentration of
the air fuel mixture does not exceed a prescribed concentration value
below a lean limit of flammability as to the fuel-gas, as well as by
means of supplying fuel-gas through the mixer in the case when a larger
amount of fuel-gas is required; further, potential fuel-gas explosion
risks in the air supply passage can be removed; what is more, since the
mixer yields an air fuel mixture of a prescribed concentration, the air
fuel control at the first gas valve for each cylinder can be simplified.

[0042]Moreover, whether or not the fuel-gas supply through the mixer is
necessary can be simply and pertinently judged in this invention, and the
second gas valve for suction air is scheduled to be opened in response to
the judgment in the case when the first gas valve for each cylinder is
fully opened and the output of the engine is being increased; thus, an
air fuel control with precision can be realized.

[0043]In addition, in the case when the engine output is lowered below a
prescribed value, then, the second gas valve for suction air is closed;
this also serves to achieve simple and precise control according to this
invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0044]The present invention will now be described in greater detail with
reference to the preferred embodiments of the invention and the
accompanying drawings, wherein:

[0045]FIG. 1 shows a two-dimensional schematic drawing of a gas engine
system as an embodiment according to the present invention;

[0046]FIGS. 2a, 2b, and 2c show a diagram for controlling fuel gas supply
according to the embodiment; and

[0047]FIGS. 3a, 3b, and 3c show a diagram for controlling fuel gas supply
according to the conventional technology.

[0048]It is noted that a related conventional technology is depicted not
in the first place but in FIGS. 3a, 3b, and 3c, as the conventional
technology can be simply explained in contrast to the presented
embodiment, i.e., the preceding figures.

DETAILED DESCRIPTION OF THE INVENTION

[0049]Hereafter, the present invention will be described in detail with
reference to the embodiments shown in the figures. However, the
dimensions, materials, shape, the relative placement and so on of a
component described in these embodiments shall not be construed as
limiting the scope of the invention thereto, unless especially specific
mention is made.

[0050]As described above, FIG. 1 shows a two-dimensional schematic drawing
of a gas engine system as an embodiment according to the present
invention; FIG. 2 shows a diagram for controlling fuel gas supply
according to the embodiment; and FIG. 3 shows a diagram for controlling
fuel gas supply according to the conventional technology.

[0051]Hereupon, an explanation is given about a gas engine configuration,
for an example, with a supercharged gas engine for driving a generator
the engine which comprises a pre-chamber for ignition; however, the
applications of the present invention are not confined to this example.
In practical terms, the gas engine may be one without a pre-chamber. As
depicted in FIG. 1, a generator 13 is a driven load as a preferable
example; as a matter of course, a driven load is not limited to a
generator.

[0052]With reference to FIG. 1, the two-dimensional schematic drawing of a
gas engine system will be explained. In the figure,

[0053]the component with Numeral 1 is an engine (a gas engine);

[0054]Numeral 4 shows a cylinder cover for each cylinder of the engine 1;

[0055]Numeral 13 shows a generator driven directly by the engine 1;

[0056]Numeral 14 shows a flywheel;

[0057]Numeral 7 shows a shaft by which an exhaust gas turbine 7a drives a
compressor 7b;

[0058]Numeral 3 shows a charging air inlet branch arm pipe that is
connected to the charge inlet of each cylinder cover 4;

[0059]Numeral 2 shows a charging air manifold that connects the charge
outlet of the compressor 7b with the charging air inlet branch arm pipe
3;

[0060]Numeral 9 shows an air cooler that cools the charging air passing
through the charging air manifold 2.

[0061]Further,

[0062]Numeral 5 shows an exhaust gas branch arm pipe that is connected to
the exhaust outlet of each cylinder cover 4;

[0063]Numeral 6 shows a main exhaust manifold, namely a concentrated
volume for exhaust gas, the volume being introduced for what is called a
constant super-charging system;

[0064]Numeral 110 shows an exhaust gas outlet pipe through which engine
exhaust gas is discharged from the outlet of the exhaust gas turbine 7a
to the atmosphere;

[0065]Numeral 11 shows an exhaust gas by-pass pipe that diverges from the
inlet of the exhaust gas turbine 7a, bypasses the exhaust gas turbine 7a,
and is connected to the exhaust gas outlet pipe 110 on the outlet side of
the turbine 7a.

[0066]Numeral 12 shows an exhaust gas by-pass valve the throat area of
which is variable;

[0067]Numeral 10a shows an air inlet passage toward the turbocharger
through which ambient air is inducted toward the cylinders via the
turbocharger compressor 7b;

[0068]Numeral 10 shows a gas-air mixer that is provided part way along the
air inlet passage 10a toward the turbocharger;

[0069]Numeral 21 shows a gas supply source line through which fuel gas
from a fuel-gas reservoir (not shown) is supplied to the engine, whereby
a second gas line 211 toward suction air induced by the turbocharger or
toward the gas air mixer, as well as a first gas line 212 toward each
cylinder are branched from the gas supply source line 21.

[0070]In relation to the above, the second gas line 211 is connected to
the air-gas mixer 10 that is provided part way along the air inlet
passage 10a toward the turbocharger, while the first gas line 212
branches, part way along the first gas line, toward a gas supply branch
arm pipe 213 at each cylinder, the pipe 213 being connected to the
charging air inlet branch arm pipe 3. The gas-air mixer is capable of
supplying fuel-gas into the suction air so that the concentration of the
air fuel mixture is kept lower than a prescribed concentration below a
lean limit of flammability as to the fuel-gas; preferably, a mixer of a
venturi type is used.

In FIG. 1, Numeral 18 shows a gas compressor that is provided on the line
212, and pressurizes the fuel-gas so that the fuel-gas passing through
the line 212 can flow into the boosted charging air;

[0071]Numeral 19 shows a second gas valve for suction air, on the second
gas line 211; this second gas valve controls fuel-gas flow through the
line 211, with on-off (open-close) movements; Numeral 20 shows a first
gas valve which is provided on the gas supply branch arm pipe to each
cylinder; the fuel-gas flow through each valve 20 is controlled by
varying its throat area so as to regulate the fuel-gas flow rate to each
individual cylinder of the engine.

Further, Numeral 15 shows an engine speed sensor that measures the
rotational speed of the engine-generator; Numeral 013 shows a load
sensor, namely, an engine load sensor; Numeral 17 shows a charging air
pressure sensor that measures the pressure at the charging air manifold
2; Numeral 16 shows a charging air temperature sensor that measures the
temperature at the charging air manifold 2; Numeral 021 shows a flow
meter that measures the fuel-gas flow rate through the second gas line
211.

[0077]The engine speed controller 24 is generally an electric governor,
and the controller regulates opening levels of the first gas valve 20 for
each cylinder, as a feedback response to the detected engine speed
signals from the engine speed sensor 15.

[0078]The air-fuel ratio controller 23 regulates opening levels of the
exhaust gas by-pass valve 12, with a means described later, in response
to the detected engine speed signals from the engine speed sensor 15, the
detected load signals from the load sensor 013, the detected charging air
pressure signals from the charging air pressure sensor 17, and the
detected charging air temperature signals from the charging air
temperature sensor 16.

[0079]During the gas engine operation, the fuel-gas from the gas supply
(source) line 21 flows into the line 212, or flows into the lines 212 and
211. The second gas line 211 leads fuel-gas to the gas-air mixer 10 where
the fuel-gas is mixed with the air flowing along the air inlet, passage
10a toward the turbocharger; whereby, the air fuel mixture is inducted
into the turbocharger compressor 7b. The mixture is pressurized into a
state of high pressure and temperature, by a substantially adiabatic
compression process through the turbocharger compressor 7b; the mixture
is cooled by the air cooler 9 and flows into the charging air inlet
branch arm pipes 3 after passing through the charging air manifold 2.

[0080]The fuel-gas that flows into the line 212, namely, the first gas
line 212, is compressed by the gas compressor 18; then, after passing
through each gas supply branch arm pipe 213 to the engine cylinders, the
fuel-gas flows to the charging air inlet branch arm pipes 3 and is mixed
with the air or the before-described air fuel mixture through the
charging air manifold 2.

[0081]On the other hand, the exhaust gas from the cylinders of the engine
1 flows through the exhaust gas branch arm pipes 5, and enters the main
exhaust manifold; then, the exhaust gas is led to the exhaust gas turbine
7a; and after driving the compressor 7b, the exhaust gas is discharged to
the atmosphere through the exhaust gas outlet pipe.

[0082]Further, when the exhaust gas by-pass valve 12 is opened in response
to a control-order signal from the air-fuel ratio controller 23 in a
manner as described later, then a part of the exhaust gas in the main
exhaust manifold bypasses the exhaust gas turbine 7a, and is released
directly toward the exhaust gas outlet pipe 11.

[0083]With reference to the engine configuration stated thus far, the
engine control method will now be described in detail.

[0084]In the first place, a conventional control method as a contrasting
example for the present invention is explained with FIGS. 3a to 3c. FIG.
3a shows a load transition as to a conventional engine; FIG. 3b shows a
transition as to an order signal that is transmitted to the first gas
valve for each cylinder; and, FIG. 3c shows a transition as to an order
signal that is transmitted to the second gas valve for suction air. As
shown in FIGS. 3a, 3b, and 3c, in the conventional control method, the
opening levels of the first gas valve for each cylinder are controlled in
response to the engine load levels so as to regulate the gas flow rates.
Thus, in the conventional way whereby the second gas valve for suction
air is not provided, only the first gas valve for each cylinder controls
fuel amounts for each cylinder; namely, the conventional way corresponds
to a manner in which the fuel order signal toward the second gas valve
for suction air is always null in the embodiment of FIG. 1.

[0085]On the other hand, FIGS. 2a, 2b, and 2c explain a control method as
an embodiment of this invention.

FIG. 2a shows a load transition as to the engine according to an
embodiment of this invention; FIG. 2b shows a transition as to an order
signal that is transmitted to the first gas valve for each cylinder; and,
FIG. 2c shows a transition as to an order signal that is transmitted to
the second gas valve for suction air. In the embodiment as shown in FIGS.
2a, 2b, and 2c, the second gas valve for suction air is opened in the
case when the fuel-gas is of a low calorific value, or the engine output
is high; and, fuel-gas is supplied to the engine both through the second
gas valve for suction air and through the first gas valve for each
cylinder. In the case when the fuel-gas is of a high calorific value, or
in the case when the output of the engine is low, the second gas valve
for suction air is closed; and, fuel-gas is supplied only through the
first gas valve for each cylinder.

[0086]To be more specific, the opening levels of the first gas valve for
each cylinder and the load levels of the engine are detected; and, the
second gas valve for suction air is opened, in the case when the opening
levels of the first gas valve for each cylinder are full (i.e., 100%) or
nearly full (i.e., more than a predetermined level) and the load levels
of the engine are increasing as shown in the neighborhood of a time point
A in FIG. 2c. Further, an air fuel mixture of a predetermined air fuel
ratio is achieved at the before-mentioned mixer; in addition, the opening
levels of the first gas valve for each cylinder are regulated so that the
air fuel ratio of an air fuel mixture just before each cylinder is at a
predetermined level (a final air fuel ratio as to an air fuel mixture
that is burned in each cylinder). In this connection, it is noted that
the opening levels of the first gas valve for each cylinder are lowered
from a full level, while the opening levels of the second gas valve for
suction air are full (100%) or near full, for example, during a time
process from a time point A to a time point B in FIG. 2c.

[0087]Further, the first gas valve for each cylinder regulates fuel-gas
flow rates with regard to the levels of the engine load, while the second
gas valve for suction air is fully (100%) opened; whereby, an air fuel
mixture of a predetermined air fuel ratio the mixture which includes air
inducted by the turbocharger, and fuel supplied through the first gas
valve for each cylinder are mixed just before each cylinder so that a
predetermined air fuel ratio for a final air fuel mixture is achieved.
Hereby, it is reconfirmed that a final air fuel mixture means the air
fuel mixture that is burned in each cylinder.

[0088]Still further, under the condition that the second gas valve for
suction air is opened and the levels of the engine load are detected,
when the detected level of the engine load becomes less than a
predetermined level, then the second gas valve for suction air is closed
and the air fuel ratio control is performed only by the first gas valve
for each cylinder, on the basis that the fuel-gas being used has a high
calorific value or the output of the engine becomes low; this situation
is depicted around a time point C in FIG. 2c.

[0089]As described above, the maximum flow rate as a threshold value of
the second gas valve for suction air is calculated in advance; and, when
the flow rate through the mentioned valve becomes lower than or equal to
the threshold value, then the second gas valve for inducted air is closed
and only the first gas valve for each cylinder regulates the fuel flow
rate. Thus, a simple control with precision can be achieved.

[0090]In the embodiment as described above, by means of the manner that
fuel gas is supplied to the suction air induced by the turbocharger only
in the case when the fuel-gas supply is greater than at a predetermined
rate, as is the case when the fuel-gas is of a low calorific value or the
engine output is high, the required fuel gas supply is achieved with
precision. Further, the described-embodiment is provided with a gas mixer
that achieves a fuel gas mixture with a concentration below a lean limit
of flammability as to the fuel-gas; and, a part of the required amount of
fuel-gas is supplied through the mixer in the case when a larger fuel
flow rate is needed; thus, the size and capacity of the gas compressor
can be reduced; further, potential fuel-gas explosion risks in the air
supply passage can be removed; what is more, since the mixer yields an
air fuel mixture of a prescribed concentration, the air fuel control at
the first gas valve for each cylinder can be simplified.

[0091]Moreover, since whether or not the fuel-gas supply through the mixer
is necessary can be simply and pertinently judged in the described
embodiment, and the second gas valve for suction air is scheduled to be
opened in response to the judgment in the case when the first gas valves
for each cylinder are fully opened and the output of the engine is
increasing, an air fuel control with precision can be realized.

[0092]In addition, in the case when the output of an engine is lowered
below a prescribed value, then, the second gas valve for suction air is
closed; serving as a simple and precise control.

INDUSTRIAL APPLICABILITY

[0093]The described embodiment provides a gas engine comprising:

[0094]a first fuel-gas supply system in which fuel-gas is mixed with
suction air inducted by a turbocharger of the engine and the fuel air
mixture is fed to the engine through the turbocharger;

[0095]a second fuel-gas supply system in which fuel-gas is supplied to a
charge air passage of each cylinder;

[0096]whereby potential fuel-gas explosion risks in the air supply
passage, at the outlet of a turbocharger compressor, can be removed;

[0097]moreover, in the case when fuel-gas of a low calorific value is
used, less power is needed to drive the gas compressor than would
otherwise be required, the gas compressor being provided in the second
fuel-gas supply system for pressurizing the fuel-gas to the charge air
passage of each cylinder;

[0098]further, the size and capacity of the gas compressor is less than
would otherwise be required.

[0099]Thus, the embodiment disclosed in this specification is useful as an
industrial technology.

Patent applications by Hajime Suzuki, Kanagawa JP

Patent applications by Hideki Nishio, Kanagawa JP

Patent applications by Yuuichi Shimizu, Kanagawa JP

Patent applications by MITSUBISHI HEAVY INDUSTRIES, LTD.

Patent applications in class Having condition responsive means to control supercharged flow to engine

Patent applications in all subclasses Having condition responsive means to control supercharged flow to engine